Gas separation processes using adsorbent beds are well known in the art. Typical adsorption-based processes include those where a gas component within a multi-component feed gas is selectively adsorbed. Of particular interest are cyclic processes wherein the adsorbed gas is removed from the adsorbent material in a reverse gas flow such as pressure swing adsorption (PSA) and vacuum pressure swing adsorption (VPSA) processes. These processes have evolved significantly over the last few years with improvements being made to the adsorbent materials, the adsorbent beds, and the overall process parameters and controls. Costs for the construction and operation of such plants are constantly being driven lower by competitive market pressures and it has become paramount to reduce the costs associated with designing, building, transporting and operating such plants by decreasing bed sizes and standardizing components. Smaller bed structures reduce the adsorbent material inventory; the size of the plant equipment, such as process vessels and surge tanks, and the overall plant footprint including the skid dimensions. Smaller skids in turn reduce transportation and installation costs.
It is therefore desirable to design new adsorbent beds for use in adsorption-based gas separation processes that are generally smaller in size; require lower fabrication costs; are easier to transport; have less maintenance and repair requirements; and are easier to load with adsorbent material. It is equally important to design adsorbent beds that, while being smaller, do not negatively affect the process flow, cycle speed, rate and volume of throughput, and overall power requirements of the process. Significant capital cost savings can be achieved using a modular and/or compact adsorbent bed structure in an adsorption-based gas separation plant.
For the purposes of the present invention, the term “modular” means reconfiguring a given frontal flow area of a conventional bed into smaller more manageable sections that fit into a housing wherein each bed unit or module is easier to load adsorbent material into, easier to handle and/or replace in the housing, and generally provide greater flexibility in design of the overall adsorption bed structure. Likewise, the term “compact” in the present invention refers to sections or units which provide intensification of the process by decreasing the adsorbent volume required for a given feed flow (by decreasing the bed depth) when cycling the process at a faster rate. In the present invention, a conventional packed bed in a gas separation plant is replaced with a plurality of modular adsorbent bed units. Individual modular adsorbent bed units, containing the adsorbent material, are combined to construct a fully sized adsorbent bed structure or vessel having the size and dimensions required for the particular plant requirements. When the modular adsorbent bed units are also made compact, then additional savings and design flexibility are possible due the reduced amount of adsorbent material required.
The present adsorption bed structure also brings together the benefits of a modular compact design utilizing low inlet void volumes, large bed frontal areas, and short bed depths (transfer lengths). It brings together these factors into a modular and scalable adsorbent bed and vessel design, requiring decreased adsorbent inventory, smaller plant equipment and hence, smaller dimensions. The compact configuration also provides higher capacity of product per unit volume of adsorbent material (i.e., increased adsorbent utilization) as compared to that obtained from a conventional packed bed. The present invention may substantially reduce the pressure drop in the adsorbent bed by optionally providing a very large flow area (frontal area) combined with shorter bed depths facilitating faster cycles in the preferred cyclic processes.